From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38EF8C43217 for ; Tue, 29 Nov 2022 01:32:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235074AbiK2BcO (ORCPT ); Mon, 28 Nov 2022 20:32:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60558 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233573AbiK2BcM (ORCPT ); Mon, 28 Nov 2022 20:32:12 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE4D643859 for ; Mon, 28 Nov 2022 17:31:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1669685473; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=9f2bXp+4ClvcwS7benxBCOAUBMUTKP2OCE5hkEkW8TU=; b=Ax0Uh+s5u5Ipb9NRlaPcnZXrSL2dDJbjXLc4rWA92HGQwx4H6AVlfLEjPg44rXWnRASY4A T+/AJPBSL0/IVl/W5LCIepPjz6A+hJzbUq2WdE7vf6gro3FeUuCCn740kJcjYdin+5qr6s IPYhdaQy4NRMpWocwa9FQ+IcsuEVUOk= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-116-B4ChANpgOCyaTpEf1UgV5Q-1; Mon, 28 Nov 2022 20:31:09 -0500 X-MC-Unique: B4ChANpgOCyaTpEf1UgV5Q-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2AFD21C051B1; Tue, 29 Nov 2022 01:31:09 +0000 (UTC) Received: from [10.22.10.34] (unknown [10.22.10.34]) by smtp.corp.redhat.com (Postfix) with ESMTP id A054F112132C; Tue, 29 Nov 2022 01:31:08 +0000 (UTC) Message-ID: <5ff3e87b-b8ce-4836-e95b-f1cbe2f5f253@redhat.com> Date: Mon, 28 Nov 2022 20:31:08 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.0 Subject: Re: [PATCH-tip v2] sched: Use kfree_rcu() in do_set_cpus_allowed() Content-Language: en-US To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira Cc: Phil Auld , linux-kernel@vger.kernel.org References: <20221129012643.1382368-1-longman@redhat.com> From: Waiman Long In-Reply-To: <20221129012643.1382368-1-longman@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/28/22 20:26, Waiman Long wrote: > Commit 851a723e45d1 ("sched: Always clear user_cpus_ptr in > do_set_cpus_allowed()") may call kfree() if user_cpus_ptr was previously > set. Unfortunately, some of the callers of do_set_cpus_allowed() > may have pi_lock held when calling it. So the following splats may be > printed especially when running with a PREEMPT_RT kernel: > > WARNING: possible circular locking dependency detected > BUG: sleeping function called from invalid context > > To avoid these problems, kfree_rcu() is used instead. An internal > cpumask_rcuhead union is created for the sole purpose of facilitating > the use of kfree_rcu() to free the cpumask. > > Fixes: 851a723e45d1 ("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") > Suggested-by: Peter Zijlstra > Signed-off-by: Waiman Long > --- > kernel/sched/core.c | 21 ++++++++++++++++++--- > 1 file changed, 18 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index f7c5253bfd21..bf9066b4f481 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2593,6 +2593,11 @@ __do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx) > set_next_task(rq, p); > } > > +union cpumask_rcuhead { > + void *cpumask; > + struct rcu_head rcu; > +}; > + > /* > * Used for kthread_bind() and select_fallback_rq(), in both cases the user > * affinity (if any) should be destroyed too. > @@ -2606,7 +2611,13 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask) > }; > > __do_set_cpus_allowed(p, &ac); > - kfree(ac.user_mask); > + > + /* > + * Because this is called with p->pi_lock held, it is not possible > + * to use kfree() here (when PREEMPT_RT=y), therefore punt to using > + * kfree_rcu(). > + */ > + kfree_rcu((union cpumask_rcuhead *)ac.user_mask, rcu); > } > > int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src, > @@ -8220,7 +8231,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask) > struct affinity_context ac; > struct cpumask *user_mask; > struct task_struct *p; > - int retval; > + int retval, size; > > rcu_read_lock(); > > @@ -8253,7 +8264,11 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask) > if (retval) > goto out_put_task; > > - user_mask = kmalloc(cpumask_size(), GFP_KERNEL); > + /* > + * See do_set_cpus_allowed() for the rcu_head usage. > + */ > + size = max_t(int, cpumask_size(), sizeof(union cpumask_rcuhead)); > + user_mask = kmalloc(size, GFP_KERNEL); > if (!user_mask) { > retval = -ENOMEM; > goto out_put_task; Peter, I would like to get this done before the next merge window. I personally prefer to define a useless union to facilitate the use of kfree_rcu(). I can also live without it and call kvfree_call_rcu() directly if this is what you want. Cheers, Longman